1) Field of the Invention
The present invention relates to an abrasive sheet and a process for producing the same. More particularly, the present invention relates to an abrasive sheet which is flexible and contains abrasive grains having a relatively large average size and uniformly dispersed in a matrix comprising an aromatic polyimide resin, and a process for producing the same.
The abrasive sheet of the present invention is employed directly or by being attached to a base of an abrading or grinding tool, to abrade or polish a surface of a hard material, or to grind or cut an inorganic or metallic material.
2) Description of the Related Arts
It is known that a flexible emery sheet is composed of a base sheet consisting of a paper sheet or cloth and abrasive grains bounded to the base sheet with a bonding agent. This conventional abrasive sheet has an unsatisfactory mechanical strength, heat resistance and abrasion property, due to the properties of the base sheet and the bonding agent, and thus is not adequate, as an industrial abrasive tool, for hard materials which resist abrasion.
U.S. Pat. Nos. 3,385,684 and 3,650,715 disclose a heat-resistant abrasive tool for super hard alloy materials. This abrasive tool is prepared by mixing a bonding agent consisting of a finely divided aromatic polyimide produced by a polymerization of pyromellitic dianhydride with an aromatic diamine, and abrasive grains consisting of diamond; molding the resultant mixture in a mold under high-temperature high-pressure conditions to provide a annular-shaped abrasive material; and bonding the annular-shaped abrasive material to a wheel-shaped base of an abrading or grinding tool, to form an abrasive grain layer.
In this conventional method, in which the abrasive material is produced by a powder-molding method, it is difficult to industrially produce an abrasive sheet having a small thickness, a high flexibility and an excellent heat-resistance.
Japanese Unexamined Patent Publication Nos. 62-74,577 and 63-237,892 disclose a flexible abrasive sheet comprising a matrix comprising an aromatic polyimide and abrasive grains having a small average size of 60 .mu.m or less uniformly dispersed in the matrix.
Nevertheless, this conventional abrasive sheet does not always have a satisfactory abrading or grinding property thereof.